I did two things: (1) I used a total of 3k resistors to regulate the voltage coming from the 5v arduino board into 3.3v so that the rfid could read the pins. This allowed the example sketch to read the UIDs of the two cards I have. (2) I modified the example sketch to only grant access to one of the cards, and after much debugging and asking Gemini for help for debugging, I finally got the program to only accept one of the cards and not the other one!